Hi Avinash,
In my opinion there is just a small difference between Share- and Like buttons. When you use a Like button the posting should appear in your feed, but visitors are not able to add a personalized text or message.
When using a Share button, visitors will be able to add a personal text or message to it before it gets shared in the Facebook timeline.
It will be interesting to see whether a posting with a personal message is performing better than a posting without (or vice versa).
https://developers.facebook.com/docs/plugins/like-button
https://developers.facebook.com/docs/plugins/share-button
Regards,
André